Frothed latex sponge rubber



compression resistance.

fiatente'd jan. 30, 19 51 FROTHED LATEX SPONGE RUBBER- Thomas H. Rogers,.lr., Akron, and Newell R; Bender, Cuyahoga Falls, Ohio, assignors toWingfoot Corporation, Akron, Ohio, 2. corporation of Delaware NoDrawing. Application March 26, 1948,

. Serial No. 17,378

14 Claims. (61. 260--723) This invention relates to frothed latex spongerubber.

Frothed sponge rubber is produced by converting rubber latex into afoam, shaping the foam, coagulating the foamed latex as by gelling, andcuring the gelled latex.

An important use of frothed sponge rubber is as a cushioning material.The cushioning properties of sponge rubber is dependent upon its abilityto be compressed. The compression resistance of sponge rubber is afunction of its density. Since the materials cost of the finished spongedepends on the cost of the rubber, compounding ingredients, and othermaterial that enter into the final product, it is desirable to replace apercentage of these materials with a rubber-latex-substitute which willproduce a sponge having the same compression resistance/weightratio asis produced by sponge'made from rubber latex without the addition ofa-rubber latex substitute hereinafter referred to as the control. v r

The use of conventional fillers such as ground rubber, etc. is notsuccessfully used as a rubber latex substitute in the production offrothed latex bonded together with latex or a suitable cement,

may be used as an inferior cushioning material in hassocks, under-rugpads, etc. uses have not proven entirely satisfactory to the spongerubber industry.

' It'has now been-discovered that scrap sponge may be added to rubberlatex and the blend frothed, gelled and vulcanized to produce a spongein which a saving in sponge ingredients is achieved.

This discovery of the utilization of scrap sponge as afiller for frothedlatex sponge, gives the industry its first practical means of disposingof its scrap in an economical manner.. However, this use'is not anobvious one because when ground scrap'sponge of a size greater than 32mesh is added to the latex, even in as low amounts as or parts of scrapper 100 parts of rubber, the weight of the finished sponge per unitvolume is increased but the compression resistance does not increaseproportionally. For example, sponge made with the addition of scrapsponge particles, of a size greater than 32 mesh weighs 2 lbs. more thandoes the control, each developing the same Since sponge is sold on acompression/weight ratio, the attempt to add However, these such as tearresistance and elongation. If these I 2 sponge particles of greater than32 mesh to rubber latex does not result in a saving of spongeingredients nor does it solve the scrap sponge problem.

It has now been discovered that a saving in sponge ingredients isobtained when scrap sponge is reduced to particles of a size that passthrough a 32 meshcreen'or pass through a screen having smaller openings.

Any rubberlatex may be used in producing the sponge rubber of thisinvention. The expression rubber latex is intended to include naturalrubber latex, as well as those of polychloroprene and the rubberybutadiene-styrene and butadiene-acrylonitrile copolymers and mixtures ofnatural and synthetic rubber latices. It is preferred, however, to usenatural rubber latex and mixtures of latices containing natural rubberlatex informing the sponge of this invention.

. The'frothed rubber latex sponge particles are produced by grindingscrap frothed latex sponge to a particle size ranging from 32 mesh orfiner in any suitable type of grinder. The 32 mesh sponge particles arethe largest size that may be used in orderto produce a frothed latexsponge having a compression/weight ratio equal to the control. Sizelarger than this act merely to increase the weight of the sponge with asubsequent loss in compression value. As the size of the particles isreduced, their value as a rubber latex substitute is increased. Thus,200 mesh sponge is preferred to mesh which, in turn, is preferred to 50mesh, and of course each of these is preferred to 32 mesh. The use ofthe smaller size sponge particles above 50 mesh is governed by theincreasing cost involved in the sponge to these smaller particle sizes.

Another unexpected observation made with respect to the use of spongeparticles of at least 32 meshisinthe fact that these sponge particlesmay be added in amounts up to 40% on the weight of the rubber to producea corresponding saving in rubber latex. For each part of rubber latexsponge particles added to the rubber latex, a corresponding saving inrubber latex is realized. When 15% of rubber latex sponge particles isadded, a, corresponding 15% saving of rubber latex is observed. It isnot desirable to add more than 40% of the latex sponge particles to therubber latex because the resulting sponge then begins to lose itsdesirable physical properties,

vtures of natural or synthetic rubber latices are prepared withsuflicient quantities of stabilizing agents for the purpose of retainingthe rubber latex and sponge particles in suspension throughout thecompounding operations. Natural rubber latex iscustomarily stabilized bythe addition of ammonia or alkali metal hydroxides, while the the latex.To the latex were added 58.4 parts of a synthetic rubber latexcontaining 60% solids (synthetic; rubber latex're'sulting fronithecopolymerization of a mixture containing 70 parts of synthetic rubberlatices are usually stabilized by 5 butadiene-l,3 and 30 parts ofstyrene) 0.61 part any one of a wide variety of organic chemicals of a50% water dispersion of ethyl zimate, 3.0 which have both stronglyhydrophilic and strongparts of a 50% water dispersion of zinc mercaplyhydrophobic radicals. A wide variety of these tobenzo'thiazole coatedwith of paraflin and compounds is known and is available commer- 3.2parts or a 50% aqueous emulsion of paraffin cially, for example,potassium ol'eate soap, rosin 10 having a melting point of 135 F. andthe batch soaps, sodium stearate, potassium lauryl sulfate, matured withslow rolling for 18 hours at 100 F. sulfonated hydrocarbons, and sodiumalkyl naph To the matured batch were added 2.01 parts of a thalenesulfate. 50% water dispersion of sym. di-beta-naphtha- The stabilizedlatex is frequently compounded lene-p-plienylenediamine, 0.28 part of a28% with a thickening agent, such as casein, gum aqueous dispersion ofcarbon black, and 2.0 parts tragacanth, or water glass. Conventionalantiof a20% aqueouls'dispersionof potassiumoleate oxidants, such asphenyl-beta-naphthylamine, and the mixture stirred at a slow speed usinga di beta-naphthylpara phenylenedia-mine; and flat type stirring unit ina frothingbowl: Water the heptyl-diphenylamines, and conventional ac wasadded to'adjust the mixture to" contain 54% celerators such as the zincsalt of mercaptobenrubber solids. zothiozole, benzo-thiazyl disulfide,zinc diethyldi- To 185 parts of this 54% aqueous dispersionthiocarbamate and tetramethylthiuram disulfide compounded natural:rubber latex was added are then added. Other modifying agents which 0.54part of 20% aqueous dispersion of potassium may be used optionally arecastor oil,.which im- 0 cleate followed by'the addition of 11 parts of20' proves the elastic properties of the sponge, carmesh frothed rubberlatexsponge scrap par,- bon blacks which are loading agents, magnesiumticles. This was then frothed in the usual man oxide and calciumsilicate which strengthen or her and 22 parts of a water dispersion of astiffen the sponge, parafiin wax which improves mixture of 2 parts ofzinc oxide and 1 part (on the the snap or rebound properties of thefinished solids) of diphenyl gu'anidine was added to' the sponge as wellas improves its resistance to com- 30 frothed compounded latex and mixedfor. 30' bustion and various dyes and coloring matters seconds. To thefrothecl mixture were added 14 for improving the appearance ofthecomposition. parts of an 18 water dispersion of sod-iums'ili- Thesponge-like compositions prepared in accofluoride andthen' mixedfor 19seconds: The: cordanoe with thi inven ion m y be s in resulting frothedlatex was oured: into a moldidentical manner to those of the prior art,and .35 445cm, X 335 m x 5 cm. i size and 56 evenly, are particularlyuseful in the fabrication. of Spaced lug h l ag' Cm in diameter d-7household furmture and automobfle. in length were impressed in thefrothand g'ella In each of the 13 examples enumerated m the tionoccurred in 7 minutes. The gelled sponge Table of Examples below the:frothed latex was cured for 10 minutes at 15 lbssteam 'res-' spongemade and tested was prepared in sub- -10 d the h Th stantially the samemanner in which the sponge. guide an n was e a e Washe sponge was ofExample 6 was prepared. Thev preparation im 16 1F? t 6? v I of thesponge in Example 6 is set forth in detail T cured il f fi d 630 gramsan as follows: developed a compression of 12 pounds. The T0 108 parts ofnatural rubber latex contain- -15 Weight per pound compression ingramswas 52-5- ing 60% solids were added 2. parts of a 20% and the pp en de yi p u p r ubi water dispersion of potassiumoleate. and 3.8 parts inchwas 0.00222 The tear resistance in pounds. ofa 20% water dispersion ofpotassium rosinate was 3.6-3.4 and the percent elongation was with slowagitation until thoroughly mixed into 150-150.-

Table of examples Amt. r wt 1b. Example sponge S81E51 Wt. gg %3123 Tear1335 Per Cent Grams Pou'mis Grams lba/zn. P0147203 Per Cent None 57011.5 49.5 0.0 4. 3-3.5 170-15 None 490 9 54.4 0001-70 3. 3-3.5 195-100None 500 10 5.0.0 0.00173 3. 03.0 240230 None 510 10 51.0 0.001313.7-2.5 200- Inthe foregoing examples,- all mesh sizes are thosespecified by the U. S. Bureau of Standards. S. Tyler Company (Cleveland,Ohio) screens were used.

In each of the foregoing examples, the compression value is obtained bydetermining the weight in pounds necessary to compress a circular areaof 50 square inches of sponge to 75% of its original thickness.

It will be noticed that when sponge particles of 20 meshare used, forexample, as setforth in Examples -8, no saving is produced. When theresults of Example 5 are compared with the results of Example 3, a netloss of 14% is involved where only of scrap sponge was added.

Thus, it can be seen that the addition of 10% of the 20 mesh scrapsponge merely added to the total weight of the finished sponge and alsorequired the addition of 4% more sponge ingredients in order to producea sponge developing the same compression resistance as was developed bythe control.

It is also interesting to note that, based on the averages, the spongein which 35 mesh scrap was added only weighed 46.25 grams per lb. ofcompressed resistance when 15% ofthe scrap was added as compared to anaverage value of 51.2 grams per lb. of compression developed for thecontrol. Thus, in addition to saving 15% of sponge ingredients by adding15% of scrap sponge particles of 35 mesh, a lighter weight sponge isproduced. This same phenomenon is also observed with respect to the 48mesh scrap sponge where an average value of 48.67 grams per lb. ofcompression is developed when 15% of the scrap sponge is added.

The advantage of adding the scrap sponge is obvious from the foregoingexamples but in addition to the advantages shown, the finished sponge isno different in appearance than the control and since the other physicalcharacteristics of the sponge containing the sponge particles are thesame as the control, then both types of sponge are equally desirableunder the same conditions of use. I

Although the invention has been described with respect to specificexamples, it is not intended that the details thereof shall be construedas limitations upon the scope of this invention except to the extentincorporated in the following claims.

We claim:

1. A frothed rubber latex sponge containing 15%, based on the weight ofrubber present, of frothed rubber latex sponge particles of 35 to 50mesh.

2. A frotheol rubber latex sponge containing 15%, based on the Weight ofrubber present, of

frothed rubber latex sponge particles of mesh.

3. A frothed rubber latex sponge containing 15%, based on the weight ofrubber present, of frothed rubber latex sponge particles of 48 mesh.

4. A frothed rubber latex sponge containing not more than about based onthe weight of rubber present, of frothed rubber latex sponge particlesof about 35 mesh to about mesh,

5. A frothed rubber latex sponge containing from about 10% to about 40%,based on the Weight of rubber present, of prevulcanized frothed rubberlatex sponge particles of about 35 mesh to about 50 mesh.

6. A frothed natural rubber latex sponge containing from about 10% toabout 40%, based on the weight of rubber present, of prevulcanizedfrothed rubber latex sponge particles of about 35 mesh toabout 50 mesh.

7. A frothed natural rubber latex sponge containing about 15%, basedonthe weight of rubber present, of prevulcanized frothed rubber latexsponge particles of about 35 mesh to about 50 mesh.

8. A frothed natural rubber latex sponge containing about 15%, based onthe weight of rubber present, of prevulcanized frothed rubber latexsponge particles of about 35 mesh.

9. A frothed rubbery polydiolefin latex sponge containing from about 10%to about 40%, based on the weight of rubber present, of frothed rubberlatex sponge particles of about 35 mesh to about 56 mesh.

10. A frothed rubbery polydiolefin latex sponge containing about 15%,based on the weight of rubber present, of frothed rubber latex spongeparticles of about 35 mesh to about 50 mesh.

11. A frothed rubbery polydiolefin latex sponge containing about 15%,based on the weight of rubber present, of frothed rubber latex spongeparticles of about 35 mesh.

12. A frothed natural rubber latex sponge containing from about 10% toabout 40%, based on the weight of rubber present, of frothed rubberlatex sponge particles of about 35 mesh to about i 50 mesh.

13. A frothed natural rubber latex sponge containing about 15%, based onthe weight of rubber persent, of frotheol rubber latex sponge particlesof about 35 mesh to about 50 mesh.

14. A frothed natural rubber latex sponge containing about 15%, based onthe weight of rubber present, of frothed rubber latex sponge particlesof about 35 mesh.

THOMAS H. ROGERS, JR. NEWELL R. BENDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,140,063 Talalay Dec. 13, 19382,288,686 Daniels July '7, 1942 2,290,613 Greenup July 21, 19422,320,425 Glaes et a1 June 1, 1943

9. A FROTHED RUBBERY POLYDIOLEFIN LATEX SPONGE CONTAINING FROM ABOUT 10%TO ABOUT 40%, BASED ON THE WEIGHT OF RUBBER PRESENT, OF FROTHED RUBBERLATEX SPONGE PARTICLES OF ABOUT 35 MESH TP ABOUT 50 MESH.